Method and apparatus for detecting vehicle distance

ABSTRACT

Stableness in detecting the distance to a preceding vehicle by calculating the distance to the preceding vehicle using reflected waves of a radar beam scanned at a scanning angle that is adjusted based on lane markers extracted from a road image obtained by a camera.

FIELD OF THE INVENTION

[0001] Generally, the present invention relates to a method andapparatus for detecting the distance between vehicles. More particularlythe present invention relates to a method and apparatus for detectingvehicle distance based on reflected waves of a beam scanned by radar.

BACKGROUND OF THE INVENTION

[0002] Recently, vehicle design trends have been moving from passivevehicle control, in which the behavior of a vehicle is controlled by adriver, to active control, in which a vehicle actively controls its ownbehavior. For example, an adaptive cruise control (ACC) system thatcontrols a vehicle's speed to automatically maintain a certain distanceto a preceding vehicle has almost been commercialized.

[0003] In order to safely provide an ACC system there must be anaccurate technique for detecting distance to a preceding vehicle.Traditionally, radar, using laser or millimeter waves has been widelyadopted to detect the distance to a preceding vehicle. Using such asystem to detect the distance, a radio wave (laser or millimeter wave)is projected to and reflected from a preceding vehicle. The reflectedbeam or wave is then detected and analyzed to calculate the distance tothe preceding vehicle.

[0004] When the vehicles are running on a flat road, the distance to thepreceding vehicle can be accurately measured. However, if the roadundulates, the preceding vehicle may become positioned vertically higheror lower than the projected scanning radar beam from the vehicleequipped with an ACC. In such a case, the following vehicle may fail todetect the distance to the preceding vehicle. Therefore, a drawback ofthe existing device is that when the vertical undulation of the road islarge a preceding vehicle falls outside the vertical width of thescanning beam. Therefore, no vehicle is detected and the vehicledistance detecting device would improperly judge the driving condition.

[0005] The information disclosed in this Background of the Inventionsection is only for enhancement of understanding of the background ofthe invention and should not be taken as an acknowledgement or any formof suggestion that this information forms the prior art that is alreadyknown to a person skilled in the art.

SUMMARY OF THE INVENTION

[0006] An exemplary apparatus for detecting distance to a precedingvehicle includes a radar for scanning a radar beam from the vehicle, ascanning angle adjustor for adjusting a scanning angle of the radar, acamera for acquiring a road image, and an electronic control unit. Theelectronic control unit is activated by predetermined software thatcomprises instructions for each step of a method for detecting distanceto a preceding vehicle.

[0007] Another exemplary method for detecting distance to a precedingvehicle useful with the present invention includes receiving a signal ofa road image from a camera and extracting lane markers from the roadimage. The method further includes adjusting a scanning angle of theradar based on the extracted lane markers and calculating a distance tothe preceding vehicle using reflected waves of a radar beam scanned atthe adjusted scanning angle.

[0008] In a further preferable embodiment, the scanning angle isadjusted by calculating a height within the image at which a horizontaldistance between the extracted lane markers is a predetermined distance.Calculating the slope of the road from the calculated height andadjusting the scanning angle of the radar based on the calculated slopeof the road.

[0009] In a still further preferable embodiment, the slope of a road iscalculated based on a difference between the calculated height withinthe image at which a horizontal distance between the lane markers is apredetermined distance and a reference height at which a horizontaldistance between lane markers is a predetermined distance.

[0010] In a still further preferable embodiment, the reference heightwithin the image corresponding to lane markers separated by apredetermined horizontal distance is an average value of the calculatedheight within the image corresponding to lane markers separated by apredetermined horizontal distance over a predetermined period.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate an embodiment of theinvention, and, together with the description, serve to explain theprinciples of the invention:

[0012]FIG. 1 is a schematic diagram of an apparatus for detectingdistance to a preceding vehicle according to an embodiment of thepresent invention;

[0013]FIG. 2 is a flowchart showing a method for detecting distance to apreceding vehicle according to an embodiment of the present invention;and

[0014]FIGS. 3A, 3B, and 3C respectively show road images and extractedlane markers when the forthcoming road is curved upward, flat, andcurved downward.

DETAILED DESCRIPTION OF THE INVENTION

[0015]FIG. 1 is a schematic diagram of an apparatus for detectingdistance to a preceding vehicle according to a preferred embodiment ofthe present invention. The apparatus includes a radar 120 for scanning aradar beam 125 from a vehicle 100. A scanning angle adjustor 130 foradjusting the scanning angle of the radar 120, a camera 110 foracquiring a road image in front of the vehicle 100, and an electroniccontrol unit (ECU) 150 activated by predetermined software. The radar120 may scan radio waves of any frequency. The camera 110 is preferablya closed-circuit digital (CCD) camera.

[0016] The scanning angle adjustor 130 adjusts the scanning angle of theradar 120 under the control of the ECU 150. The scanning angle adjustor130 can be realized by a person skilled in the art, for example, byusing a motor and gears. The ECU 150 can be realized by one or moreprocessors activated by predetermined software, and the predeterminedsoftware can be programmed to perform each step of a method fordetecting a vehicle distance according to a preferred embodiment of theinvention.

[0017] A method for detecting distance to a preceding vehicle ishereinafter described with reference to FIG. 2. The method is explainedwith reference to the case that the vehicle 100, equipped with the radar120, detects the distance to a preceding vehicle 190 using the radar120. Initially, at step S210, the ECU 150 receives a signal of a roadimage from the camera 110. Subsequently, at step S215, the ECU 150extracts lane markers from the image of the road. Preferably at leasttwo adjacent lane markers are extracted, at step S215. Step S215, theextraction of lane markers from the road image, can be realized by aperson of ordinary skill in the art in a variety of fashions. Forexample, the lane markers can be extracted based on brightness of pixelson the image.

[0018] Following extraction of the lane markers, the ECU 150 adjusts thescanning angle of the radar 120 based on the extracted lane markers, atstep S220. Subsequently, at step S240, the ECU 150 calculates a distanceto the preceding vehicle 190 using reflected waves of the radar beam 125scanned at the adjusted scanning angle. The step S240 of calculating adistance to the preceding vehicle 190 using reflected waves of a radarbeam 125 is obvious to a person of ordinary skill in the art.

[0019] Step S220, the adjusting of the scanning angle of the radar 120is hereinafter described in more detail. Initially, at step S225, theECU 150 calculates a height H within the image in which a horizontaldistance between the extracted lane markers is a predetermined distanceD. The predetermined distance D may be set by a person of ordinary skillin the art with reference to factors related to the camera 110, such asan exposing direction of the camera 110 and size of the road image.

[0020]FIGS. 3A, 3B, and 3C show road images and extracted lane markerswhen the forthcoming road is curved upward, flat, and curved downward,respectively.

[0021]FIG. 3B represents the case where the forthcoming road is flat. H0is set as a reference height within the image corresponding to lanemarkers separated by a predetermined distance D. When the forthcomingroad is curved upward (refer to FIG. 1 and FIG. 3A), the position oflane markers 310 in the road image, separated by the predetermineddistance D, is moved upward. The position within the image of the lanemarkers, where the distance between the lane markers is thepredetermined distance D, is H1. When the road curves upward, H1 ishigher than H0 within the image. To the contrary, when the forthcomingroad is curved downward (refer to FIG. 3C), the position of the lanemarkers 330 separated by the predetermined distance D in the road imageis moved downward. In this case, a height H3 at the predeterminedhorizontal distance D between extracted lane markers 330 becomes lowerthan the reference height H0.

[0022] After the height H is calculated at step S225 (FIG. 2), the ECU150 calculates, at step S230, the slope of the forthcoming road based onthe calculated height H. Therefore, the slope of the forthcoming road iscalculated based on a difference between the calculated height H and areference height H0.

[0023] The step S230 of calculating the slope of the road, based on thedifference between the calculated height H and a reference height H0,can be realized by a person of ordinary skill in the art. For example,the relation between the slope of the road and the difference of the twoheights, which can be obtained by simple experiments, can be formalizedas a lookup table.

[0024] In the above, the reference height H0 is explained as a height atwhich the horizontal distance between the extracted lane markers is thepredetermined distance D when the forthcoming road is flat. The value ofsuch reference height H0 may be varied according to a variety offactors, such as camera angle and the like. Thus the value of thereference height H0 for a specific vehicle may be set as a constant by aperson of ordinary skill in the art, considering factors related to thespecific vehicle's specification. However, it is more preferable thatthe reference height H0 is an average value of the calculated height Hof extracted lane markers over a predetermined period. This feature canreduce error in calculation of the slope of the road in the case thatthe exposed direction of the camera 110 is changed by arbitrary reasonsor factors. Furthermore, when the actual distance between lane markerson the road is varied, this feature can reset the value of the referenceheight H0 as an appropriate value to the varied distance of actual lanemarkers after a period of time. The predetermined period may be set by aperson of ordinary skill in the art with reference to average undulationof the road on which the vehicle 100 runs.

[0025] Referring back to FIG. 2, when the slope of the forthcoming roadis calculated, at step S230, the ECU 150 adjusts the scanning angle ofthe radar 120, at step S235, based on the calculated slope of theforthcoming road. The amount of adjustment of the scanning angle may becalculated by a person of ordinary skill in the art. For example, theamount of adjustment may be calculated proportionally to the slope ofthe forthcoming road.

[0026] While this invention has been described in connection with whatis presently considered to be the most practical and preferredembodiment, it is to be understood that the invention is not limited tothe disclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

[0027] Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” or variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

What is claimed is:
 1. A method for a vehicle equipped with a radar fordetecting distance to a preceding vehicle, comprising: receiving asignal of a road image from a camera; extracting lane markers from theroad image; adjusting a scanning angle of a radar based on the extractedlane markers; and calculating a distance to a preceding vehicle usingreflected waves of a radar beam scanned at the adjusted scanning angle.2. The method of claim 1, wherein said adjusting a scanning anglecomprises: calculating a height within said image at which a horizontaldistance between the extracted lane markers is a predetermined distance;calculating a slope of the road based on the calculated height; andadjusting a scanning angle of the radar based on the calculated slope ofthe road.
 3. The method of claim 2, wherein said calculating a slope ofa road calculates the slope of the road based on a difference betweenthe calculated height and a reference height.
 4. The method of claim 3,wherein the reference height is an average value of the calculatedheight over a predetermined period.
 5. An apparatus for a vehicle fordetecting distance to a preceding vehicle, the apparatus comprising: aradar for scanning a radar beam from the vehicle; a scanning angleadjustor for adjusting a scanning angle of the radar; a camera foracquiring a road image; and an electronic control unit activated bypredetermined software wherein said predetermined software comprisesinstructions for: receiving a signal of a road image from the camera;extracting lane markers from the road image; adjusting the scanningangle of the radar based on the extracted lane markers; and calculatinga distance to the preceding vehicle using reflected waves of the radarbeam scanned at the adjusted scanning angle.
 6. The apparatus of claim5, wherein said adjusting scanning angle comprises: calculating a heightat which a horizontal distance between the extracted lane markers is apredetermined distance; calculating slope of a road based on thecalculated height; and adjusting a scanning angle of the radar based onthe calculated slope of the road.
 7. The apparatus of claim 6, whereinsaid calculating slope of a road calculates the slope of the road basedon a difference between the calculated height and a reference height. 8.The apparatus of claim 7, wherein the reference height is an averagevalue of the calculated height over a predetermined period.
 9. A methodfor calculating distance to a preceding vehicle, comprising: acquiringan image of a forthcoming road; adjusting a scanning angle of a radar inaccordance with said image of a forthcoming road; and calculating adistance to a preceding vehicle based on reflected radar waves from saidradar projected at said adjusted scanning angle.
 10. The method of claim9, wherein said image includes lane markers.
 11. The method of claim 10,further comprising, before said adjusting, extracting lane markers fromsaid image.
 12. The method of claim 11, further comprising before saidcalculating a distance, calculating a height within said imagecorresponding to lane markers separated by a horizontal distancesubstantially equal to a predetermined distance.
 13. The method of claim12, further comprising, before said calculating a distance, calculatinga slope of the road based on said calculated height within said image.14. The method of claim 13, wherein said calculating of a slope of theroad is based on the difference between the calculated height withinsaid image and a reference height corresponding to lane markersseparated by a predetermined distance.
 15. The method of claim 13,wherein said calculating of a slope of the road is based on an averagevalue of the calculated height within said image corresponding to lanemarkers separated by a predetermined distance of at least two sets oflane markers.